Microwave Patch Antenna with SnO₂-Filled Grounded Vias for Passive RFID Hydrogen Sensing

This work introduces a low-profile hydrogen (H₂) sensing microwave system designed for seamless integration onto metallic infrastructures, commonly needed in industrial environments. The sensor is based on a microstrip patch antenna engineered with grounded vias located at its radiating edges, corresponding to regions where the electric-field intensity is the highest. These grounded vias are filled with tin oxide (SnO₂), whose permittivity undergoes pronounced variation upon exposure to hydrogen, thereby inducing a detectable shift in the antenna’s resonant frequency. To enable practical deployment in distributed monitoring systems, a vertical array composed of two engineered patch antennas with a suitable feeding network is implemented, allowing the sensor to function as the radiating element of a passive RFID tag. This architecture supports remote, battery-less, and real-time H₂ detection within the safety-critical 0–2% concentration range through backscatter interrogation.